Effects of constant rate infusion of lidocaine and ketamine, with or without morphine, on isoflurane MAC in horses
Article first published online: 13 JUN 2011
© 2011 EVJ Ltd
Equine Veterinary Journal
Volume 43, Issue 6, pages 721–726, November 2011
How to Cite
VILLALBA, M., SANTIAGO, I. and DE SEGURA, I. A. G. (2011), Effects of constant rate infusion of lidocaine and ketamine, with or without morphine, on isoflurane MAC in horses. Equine Veterinary Journal, 43: 721–726. doi: 10.1111/j.2042-3306.2010.00355.x
- Issue published online: 11 OCT 2011
- Article first published online: 13 JUN 2011
- [Paper received for publication 14.07.10; Accepted 19.11.10]
Reasons for performing study: Lidocaine and ketamine are administered to horses as a constant rate infusion (CRI) during inhalation anaesthesia to reduce anaesthetic requirements. Morphine decreases the minimum alveolar concentration (MAC) in some domestic animals; when administered as a CRI in horses, morphine does not promote haemodynamic and ventilatory changes and exerts a positive effect on recovery. Isoflurane-sparing effect of lidocaine, ketamine and morphine coadministration has been evaluated in small animals but not in horses.
Objectives: To determine the reduction in isoflurane MAC produced by a CRI of lidocaine and ketamine, with or without morphine.
Hypothesis: Addition of morphine to a lidocaine-ketamine infusion reduces isoflurane requirement and morphine does not impair the anaesthetic recovery of horses.
Methods: Six healthy adult horses were anaesthetised 3 times with xylazine (1.1 mg/kg bwt i.v.), ketamine (3 mg/kg bwt i.v.) and isoflurane and received a CRI of lidocaine-ketamine (LK), morphine-lidocaine-ketamine (MLK) or saline (CTL). The loading doses of morphine and lidocaine were 0.15 mg/kg bwt i.v and 2 mg/kg bwt i.v. followed by a CRI at 0.1 mg/kg bwt/h and 3 mg/kg bwt/h, respectively. Ketamine was given as a CRI at 3 mg/kg bwt/h. Changes in MAC characterised the anaesthetic-sparing effect of the drug infusions under study and quality of recovery was assessed using a scoring system.
Results: Mean isoflurane MAC (mean ± s.d.) in the CTL, LK and MLK groups was 1.25 ± 0.14%, 0.64 ± 0.20% and 0.59 ± 0.14%, respectively, with MAC reduction in the LK and MLK groups being 49 and 53% (P<0.001), respectively. No significant differences were observed between groups in recovery from anaesthesia.
Conclusions and clinical relevance: Administration of lidocaine and ketamine via CRI decreases isoflurane requirements. Coadministration of morphine does not provide further reduction in anaesthetic requirements and does not impair recovery.